typescript - Diff between ViewEncapsulation.Native, ViewEncapsulation.None and ViewEncapsulation.Emulated

Question

Can some one explain what's the difference between ViewEncapsulation.Native, ViewEncapsulation.None and ViewEncapsulation.Emulated in angular2.

I tried to google it and read some articles, but I'm not able to understand the difference.

Below I have two components Home (home.ts) i.e. parent component and MyComp (my-comp.ts). I want to define styles in the parent that are being used in the child component.

Should I use ViewEncapsulation.Native or ViewEncapsulation.None

home.ts

import {Component, ViewEncapsulation} from 'angular2/core';
import {MyComp} from './my-comp';
@Component({
  selector: 'home',  // <home></home>
  providers: [
  ],
  directives: [
    MyComp
  ],
  styles: [`
    .parent-comp-width {
       height: 300px;
       width: 300px;
       border: 1px solid black;
     }
    `],
  template:`
    <my-comp></my-comp>
    <div class="parent-comp-width"></div>
  `,
  encapsulation: ViewEncapsulation.Native
})
export class Home {
}

my-comp.ts

import {Component} from 'angular2/core';

@Component({
  selector: 'my-comp',  // <home></home>
  template: `
  <div class="parent-comp-width">my-comp</div>
  `
})
export class MyComp {
}

Answer 1

update If you want styles that are added to Parent applied to Child you need to set ViewEncapsulation.None in the Child component so it doesn't prevent styles to bleed in.

Emulated and Native are just two different ways to prevent styles to bleed in to and out from components. None is the only one that allows styles to cross component boundaries.

original

• ViewEncapsulation.None is simple no encapsulation

• ViewEncapsulation.Emulated (currently the default in Angular2)
  adds attributes to component tags and child elements and manipulates the CSS (adding the attributes to the selectors) added to the page so the styles don't bleed into each other - to keep styles scoped to the components where they are added even though the styles are all added collected in the head of the page when components are loaded.

• ViewEncapsulation.Native creates custom elements with shadow DOM where the browsers native implementation ensures the style scoping.
  If the browser doesn't support shadow DOM natively, the web-components polyfills are required to shim the behavior. This is similar to ViewEncapsulation.Emulated but the polyfills are more expensive because they polyfill lots of browser APIs even when most of them are never used. Angulars Emulated emulation just adds the cost for what it uses and is therefore much more efficient for Angular applications.